A new form of bullying known as "happy slapping" where pupils gang up on a victim, assault them and use their mobile telephones to video the attack is spreading in schools.
Doctors and children's charities said they were concerned about the emotional and physical damage which the craze could cause to pupils.
The bullying takes its inspiration from violent reality videos, such as those produced in the United States featuring tramps who have been paid to fight with one another.
Pupils usually share the videos at school by making wireless connections between their phones. In some cases they have emailed the videos to friends and posted them on websites.
One London teacher said: "The school fight you used to deal with is now a media event, with an audience around the whole school and, potentially through email, the whole of London and the country."
He said he had been shown clips of girls fighting at a bus stop outside a school and two boys apparently brandishing weapons and covered in blood.
A pupil told him: "It tells other schools how hard your school is. It's proof. Then they try and send you something worse, go one better."
Headteachers' leaders said the craze, which began in London secondary schools last year, was another reason why mobile telephones should be banned from schools.
John Dunford, general secretary of the Secondary Heads Association, said:
"People are very worried about mobiles being used as a tool for bullying."
The bullies tend to attack younger pupils, but teenagers report that they have seen videos in which adult men and women have been slapped by gangs of youths on public transport.
The London teacher said: "The standard format is a slap round the head. The perpetrator gets another pupil to video it. If the happy slap is a planned event, there is likely to be a huge crowd emerging from the woodwork, out of classrooms from along the corridor.
"As you wade your way through the crowd, the pack of observers hold their phone cameras out and there's a frenzy of snapping."
Teenagers have been arguing about the craze on youth websites. While some said they had found the clips amusing, most were scathing of the pupils who carried out the pranks.
"Happy slaps are evil," one said. "To make it worse it's recorded on a camera phone and passed around, and the slaps are bloody hard. These boys even slap girls and women, it takes the piss."
Another said: "I was at my friend's birthday when these boys came and happy slapped this boy so hard. My friend grabbed him and took him off the bus. I hate it. It just gets on my nerves so much."
Professor John Pierce, a child health expert in Cornwall, said the assaults were obviously harmful to children both physically and mentally. "I think it's unlikely to cause long-term physical damage, though it depends where the children are hit and how hard," he said.
"It should be a police matter - that is what would happen if it took place between adults."
The anti-bullying charity Kidscape has received numerous calls about bullying involving mobile telephones and websites, although none yet about happy slapping.
A spokeswoman said: "What is scary about this is they do not realise that they could kill someone. For them it's just a bit of fun, but for the victim it's terrifying and when they put it on the internet it could drive some children to feel suicidal."